There are many thousands of oil wells over the surface of the earth that are drilled and completed in unconsolidated sand, i.e. crumbly sandstone. In such wells, sand does not necessarily precipitate to the bottom of the well, but instead may remain in suspension and is pumped up, if not free flowing, with the oil. As a result, most mechanical parts as valves, bearings, pistons, cylinders, etc. wear out prematurely under such conditions. Accordingly, the sand must be filtered out from the oil, preferably in the well. Petroleum companies have spent large sums of money in trying to find a suitable solution to the sand problem, but heretofore there has been no satisfactory method or long lasting device for preventing the entry of sand into the tube string and eventually into the suction pipe of the pump, or other works, and for cleaning sand screens quickly without bringing the screen to the surface for cleaning and then returning it to the bottom of the well.
In the construction of the present day sand screen, the mode of operation is such that the sand screen must be replaced for one of two reasons. The first occurs when the sand screen has developed limited flow capacity as a result of screen gauge reduction from plugging or scale build-up. The second occurs when the gauge of the sand screen becomes larger than the original design which allows sand into the production string. The disclosed invention eliminates the need to replace the sand screen when it has limited flow capacity. Thus, the intent of this sand screen cleaning system is to eliminate the cost of loss in production and the cost of re-work operation which include equipment and manpower in removing and replacing a sand screen with limited flow capacity.
U.S. Pat. No. 2,837,032 discloses an oil well foam and wire coil filter, but that filter is quite sophisticated and expensive to manufacture, and is not adjustable to be opened for backwashing a cleaning liquid, as water, to clean the clogged filter. Another attempted solution was a spring filter as disclosed in U.S. Pat. No. 3,754,651, but because no spacers are apparent between the helical filter elements, the elements would have to be held in slight tension to separate the helical filter elements during filtering. Thus that filter could not be used as an oil well filter on which high compressive loads may be placed. Likewise no spring valve can be utilized therein to strengthen the compressive capabilities for converting the filter to one for use in wells. Also, the spring filter of U.S. Pat. No. 3,179,116 is incapable of being strengthened to use in wells. Any compressive force on the triangular spring elements would cause them to collapse, and further the coined depressions for separating the spring elements would cause the spring elements to flex with a load thereon causing displacement of the adjacent coils and variations of the gauge therebetween.
Thus, new and better methods for forming and assembling helical spring sand filters, and better self-cleaning helical spring sand filters are required for mounting on the lower end of a tubing string extending down into a well to the oil containing sand strata.
The disclosed inventions are improvements over those of Assignee's U.S. Pat. Nos. 3,901,320 (166-311) and 3,937,281 (166-233).